Obesity, defined as an excess of body fat or adipose tissue, is a condition that adversely affects human health. The clinical problem of excessive adipose tissue resides in its strong association with a number of chronic diseases such as type II diabetes, metabolic disorders and coronary heart disease. The etiology of obesity is complex, resulting from the combined effect of a network of genes, and the influences of diet, age, gender and exercise. Aging is also a major contributor. A general increase in fat mass typically occurs between the third and seventh decades of life. Interestingly, obesity and related metabolic diseases have been shown to be associated with a state of chronic inflammation characterized by abnormal cytokine production and other stress-induced molecules. Aging is also accompanied by a general decline in immune function and a concomitant age-dependent up-regulation of the inflammatory response. The hypothesis of this project is that evolutionary conserved .qenetic pathways regulate age related changes in triglyceride storage and innate immune function through the utilization of common regulatory molecules, and that these pathways can be identified by QTL analyses of triglyceride levels and immune responses in Drosophila melano,qaster. Both triglyceride storage and immune response are complex polygenic traits, relying on the interaction of a large number of genes. Therefore, a quantitative genetic approach offers the most promise for identifying pleiotropic loci that contribute to the age-related changes in these traits. The specific aims of this project are to: 1) Map chromosomal regions (quantitative trait loci or QTL) at which natural genetic variation affects agerelated changes in triglyceride storage and immune response of D.melanogaster. 2) Identify candidate genes affecting age-related changes in both triglyceride storage and innate immune response. Candidate genes will be identified by refining the position of QTL using quantitative complementation to deficiencies and fine-scaled mapping with advanced intercross lines. 3) Test the causal relationship between natural sequence variation in candidate genes and phenotypic variation in age-related changes in triglyceride storage and innate immune response. To do this, we will use linkage disequilibrium mapping of a sample of alleles from a randomly mating population. This study will identify genes and genetic networks affecting age related changes in triglyceride storage and immune response and elucidate the extent to which these traits are regulated by pleiotropic loci. Identification of these genes will likely provide new models for human obesity and could serve as genetic markers for age-specific risk assessment. In addition, the genes identified could be potential targets for the treatment and prevention of age-related metabolic and immune dysfunction. Moreover, knowledge of the nature and frequency of causative genetic polymorphisms will lead to a better understanding of the mechanisms that maintain genetic variation in these traits in natural populations.